1. Field of the Invention
The present invention relates to a traveling-wave tube, and more particularly, to a traveling-wave tube having a conduction cooling type heat radiating structure in its collector unit.
2. Description of the Related Art
A traveling-wave tube has such main components as an electron gun unit for generating an electronic beam; a high-frequency circuit for amplifying high-frequency power through the interaction of the electron beam generated by the electron gun with a high-frequency electric field; and a collector unit for collecting the electron beam which has finished the interaction in the high-frequency circuit. The collector unit generates an enormous amount of heat when it converts kinetic energy that is possessed by the electron beam into thermal energy with the potential on a collector electrode itself. For this reason, the collector must be cooled down by some kind of heat radiating structure.
Conventionally, there are a variety of heat radiating structures. One such heat radiating structure is the conduction cooling type which conducts heat generated in a collector unit to a radiator that is disposed in close contact with the outer peripheral wall of the collector through an insulating material, such as ceramic, under the action of thermal conduction, and dissipates the heat to a heat sink or a substrate external to a traveling-wave tube.
FIGS. 1, 2 are cross-sectional views each illustrating the structure of a conduction cooling type heat dissipator in a collector unit for a conventional traveling-wave tube disclosed in JP-7-45207-A. A heat dissipator illustrated in FIG. 1 comprises cylindrical ceramic 103 disposed outside of and in contact with collector core 101; radiator 102 disposed outside of and in contact with cylindrical ceramic 103; and heat sink 104 on which radiator 102 is directly mounted. A heat dissipator illustrated in FIG. 2, in turn, comprises cylindrical ceramic 103 disposed outside of and in contact with collector core 101; radiator 102 disposed outside of and in contact with cylindrical ceramic 103; and heat sink 104 on which radiator 102 is directly mounted. Cylindrical ceramic 103 is formed with slit 106 extending in an axial direction. The top of radiator 102, opposite to heat sink 104, is formed with a slot extending in the axial direction and two protrusions, such that the protrusions of radiator 102 are fastened with a screw.
In the structure of the conventional traveling-wave tube illustrated in FIG. 1, entire collector core 101 and cylindrical ceramic 103 are covered with radiator 102 without fastening feature, so that each component must be made with a high dimensional accuracy and therefore exhibits low productivity. On the other hand, in the structure which fastens cylindrical ceramic 103 by radiator 102 itself on the opposite side from heat sink 104, the heat dissipator requires screw fastening feature which protrudes on the top of radiator 102. Due to this fastening feature, a waveguide or the like cannot be directly installed on the top of radiator 102. In addition, this fastening feature applies a force only to the protrusions, and therefore experiences difficulties in fastening the entire insulator, thus causing a lower thermal conductivity.